Piano soundboard



March 28,1967 f H, K, GRAVE-s 3,311,009

PIANO SOUNDBOARD Filed Feb. 2l, 1966 f rapidly enough and the tone will be thin.

the bridge.

United States Patent C) 3,311,009 l PIAN() SOUNDBARD Howard K. Graves, 6633 Somerset Drive, Cleveland, Ohio 44141 Filed Feb. 21, 1966, Ser. No. 528,908 7 Claims. (Cl. 8f3-492) This invention relates to soundboards for stringed musical instruments, and more particularly relates to an improved soundboard for pianos.

The soundboard of a piano radiates into the air the sound energy of the vibrating strings. The soundboard serves as an acoustical coupling between the strings and the air. The soundboard is driven by the strings through a bridge that forms one of the vibrational ends of the strings.

The vibrating strings must be supported at the bridge by a proper degree of acoustical stiffness. This acoustical stiffness regulates the rate at which energy is transferred from the vibrating strings to the air. Each string must be supported at the bridge with a proper degree of acoustical stiffness for the tone to be pleasing. lf the degree of stiffness is not sufficient, the energy of the string will be transferred too rapidly to the air and the tone will sound like a dull thud. If the degree of stiffness is exces-v sive, the energy of the string will not be transferred The proper degree of stiffness is a function of both the frequency of the string and the tension of the string. Higher pitched strings require more stiffness 4than lower pitched strings and higher tensioned strings require more stiffness than lower tensioned strings.

The soundboard of a conventional piano performs two functions: it radiates sound and it supports the strings with the required degree of acoustical stiffness. The conventional soundboard is a wooden, structural diaphragm that is secured to the frame or case of the instrument. The required acoustical stiffness at the bridge is provided by the structural plate rigidity of the diaphragm. The soundboard radiates sound energy into the air by vibrating diaphragmatically, with the bridge as a driving point.

The requirements that the soundboard both radiate sound and provide a stiff support for the strings are mutually conflicting. A soundboard that is sufficiently stiff to support the strings With the required degree of acoustical stiffness is not sufficiently light and free to be able to respond faithfully to the upper harmonics of the vibrating strings. The conventional soundboard is thus not an optimum radiator of sound. Y

In addition, the diaphragmatic mounting of the structural soundboard doesnot provide the optimum degree of acoustical stiffness for every string along the length of The stiffness at any particular point along the bridge is dependent upon the distance of that point from the edges of the soundboard. This degree of stiffness may not necessarily be optimum for that particular point in the string scale. For example, the treble register is quite stiff, the center register is less stiff, but the bass register which should be still less stiff, is more stiff due to its increased proximity to the edge of the soundboard. Therefore, the bass notes of a conventional piano are normally too stiffly supported.

Various means have been employed in an attempt to decrease the acoustical stiffness of the support for the bass strings. One means that is employed is too overstring the bass register with a separate bass bridge that is mounted away from the edge of the soundboard. The result is only partially satisfactory because an optimum gradaton of stiffness is not achieved. Another means that is employed in upright and small grand pianos is to cantilever the bass bridge, The cantilever mounting permits the bridge to be' mounted to the soundboard away from the edge of the ICC soundboard. However, the cantilever mounting forms a resilient rather than a rigid coupling between the bridge and the soundboard that prevents the strings from efiiciently driving the soundboard.

This invention discloses a novel method of constructing a piano in which means for radiating the sound and means for providing the acoustical stiffness at the bridge are accomplished by two different members. The separation of the soundradiating means from the stiffness means allows the sound radiator to be designed to be a light, efficient, responsive radiator of sound, and allows the acoustical stiffnessalong the length of the bridge to be designed to Ibe optimum for each string. A greatly improved balance of sound radiating properties and proper gradation of stiffness are thus possible with this invention.

In this invention the sound board is mounted acoustically relatively tightly to the frame or ease around the entire periphery of the soundboard. The soundboard thus vibrates, at least in its fundamental mode, in a generally diaphragmatic manner under the driving action of the bridge.

The soundboard must be acoustically relatively tightly coupled to the frame to be able to vibrate in a generally diaphragmatic manner. The soundboard may be rigidly coupled to the frame, in which case the coupled periphery does not translate or rotate relative to the frame, and the diaphragmatic vibratory motion is accomplished by the flexure of the soundboard itself in the vicinity of the edge. The soundboard may |be pivotally coupled to the frame around its periphery, in which case the soundboard does not translate but rotates along the periphery. The soundboard may be stiffy coupled to the frame around its periphery. The stiff coupling allows the generally fixed periphery of the soundboard to vibrate, both translatory and rotary, although such vibration of the periphery is necessarily small.

The soundboard may be mounted to the frame in a composite manner and still be acoustically relatively tightly coupled to the frame and still vibrate in a generally diaphragmatic manner. For example, the soundboard may be rigidly mounted to the frame along the edge parallel to the hammer strike line and opposite to the bridge, and be pivotally mounted to the frame along the edge adjacent to the bridge. Various combinations of rigid mounting, pivotal mounting, and stiff mounting may be employed to achieve an acoustically optimum mounting of the soundboard.

,The relative gradations of the tightness of the coupling of the edge of the soundboard to the frame are, in decreasing order of tightness: rigid, pivoted and stiff. For t-he purpose of definition, a relatively tight coupling between.

the edge of the soundboard and the frame is a coupling in which the general amplitude of vibration of the edge of the soundboard is small in comparison to the general amplitude of vibration of the bridge. A relatively tight coupling between the edge of the soundboard and the frame can also be defined as a coupling that sufficiently restrains t-he edge of the soundboard so that the soundboard vibrates, at least in its fundamental mode, in a generally diaphragmatic manner.

In this invention the acoustical stiffness at the bridge is provided by stiffness means external to the structure of the soundboard. This external stiffness means is disposed between the bridge and an extension of the frame that lies opposed to the bridge. The variation in the stiffness along the length of the bridge, to provide for the varying stiffness requirements throughout the string scale, may be accomplished by varying the stiness constant of individual stiffness means, by varying the spacing between individual stiffness means, or by linearly varyingy the stiffness of a continuous stiffness means.

In this invention the soundboard is intended to be a light, responsive radiator of sound. Such a low mass soundboard must be structurally relatively resilient and therefore can not provide any signicant acoustical stiffness at theV bridge. Furthermore, in this invention the soundboard is intended not to contribute substantially to the acoustical stiffness at the bridge because the required stitness is intended to be provided primarily by the external stiffness means.

The soundboard, not being a structural member, may be made only sufficiently strong to withstand the inertial and air loads caused by vibrating. The soundboard may be made from a variety of materials and may be constructed in a variety of manners. The soundboard may be made from wood, metal, plastic, foamed plastic or paper.

In this invention the major portion of the acoustical stiffness at the bridge is provided by an external stiffness means. The soundboard, which is acoustically relatively tightly coupled to the frame, contributes little to the acoustical stiffness at the bridge.

This invention has several major advantages when applied to a piano. One advantage of this invention is that the gradation of stiffness along the entire length of the bridge can be optimum. The grad-ation of stiffness can be optimum because the stiffness is controlled by the external stiiness means and, since the soundboard contributes little to the total stiffness, the proximity ofthe bridge to the edge of the soundboard is of little significance.

` Another advantage of this invention is that the soundboard may be of low mass because the soundboard does not structurally support the strings at the bridge. A low mass soundboard responds more freely to the harmonics of the vibrating strings than does a normal structural soundboard, and thus produces a more pleasing tone. Y Prior art teaches the placing of force-producing members under the bridge and soundboard of a piano. The purpose of these force members is to apply pressure to the bridge to counteract the downbearing pressure of the strings. This counter force prevents the soundboard from gradually sagging with time under the sustained downbearingpressure of the strings. The prior art teaches the `addition of these force members to pianos of generally conventional soundboard construction in which the acoustical stillness at the bridge is provided primarily by the structural stiffness of the soundboard itself.

A preferred embodiment of the invention is illustrated in the accompanying drawing in which:

FIGURE l is a plan view 'of the piano frame-stringsoundboard system showing the layout of the frame, the strings and the soundboard.

FIGURE 2 is a sectional view along line 2-2 in FIG- URE l showing a soundboard that is'rigidly mounted to FIGURE 3 is a sectional view along line 2 2 in FIG- URE 1 showing asoundboard that is pivotally mounted and stiily mounted to the frame.

. FIGURE 4 is an enlarged detail section along line 2-2 in FIGURE l showing the stiffness means.

Referring to the drawings, FIGURE 1 shows a framestring-soundboard. system constructed in accordance with the principles ofthis invention. A frame 10, such aS might be used in a piano, supports a full complement of musical strings indicated in general by numeral 11. The tailend of each of the strings is attached by means of a hitch pin 12 to the hitch portion 13 of frame 10'.. The head end of each of the strings is attached to frame by means of a tuning pin 14.

The strings -11 vibrate between xed bar 15, that is a part of frame 10, and vibrating bridge 16. Bridge 16 is secured with glue to soundboard 17. Soundboard 17 is acoustically tightly coupled to frame 1t) along mounting Iedges 18, 19, 20 and 21.

The acoustical stiffness at bridge 16 is provided by the plurality of stiffness members 22 that are disposed in an acoustically optimum manner between the soundboard 17 under bridge 16 and a portion ofthe frame 23 that extends in spaced proximity to bridge 16.

The stitlness members 22 provide the acoustical stiftness with which bridge 16l must be supported to produce a pleasing tone. The stiilness members may be placed one under each string, one under each group of strings, or a single stiliness member could be extended along the entire length of the bridge.

FIGURE 2 shows one method of relatively tightly coupling soundboard 17 along edges 13, 19, 20 and 21 to frame 10. The soundboard 17 is rigidly secured with adhesive to mounting projection 24 on frame 10. The securing of the soundboard directly to the frame forms a rigid coupling that prevents the edges of the soundboard from vibrating or rotating relative to the frame.

FIGURE 3 shows two other coupling methods, used in conjunction with each other, to relatively tightly couple the edges 18, 19, 20 and 21 ofthe soundboard 17 to the frame 1t). Edge 18 of soundboard 17 is stily coupled to frame 1l) by means of stitl: member 26. Stiff member 26 is secured with adhesive to edge 18 of soundboard 17, and is secured with adhesive to projection 24 on frame 1'. Stiff member 26, because of its own slight cantilever deflection, allows the edge 13 to vibrate in a highly restrained manner. Edge 26 of soundboard 17, is pivotally secured to frame 10 by ymeans of a flexural pivot member 2S. Flexural pivot member 25 is secured as with screws to frame 1t). The flexural member 25 permits the soundboard to pivot generally about edge 20, yet fully restrains its translatory vibratory movement in a plane normal to the strings.

FIGURE 4 is an enlarged detail of the stiffness means. String 11 passes over bridge 16. The slight downward angle, known as the downbearing of string 11 after it passes over bridge 16, causes the string to be tightly coupled to bridge 16 at point 27. Bridge point 27 must be provided with the proper degree of acoustical stiffness for the musical tone to be pleasing. The acoustical stitiness at bridge point 27 is provided by a stiff member 22 that is disposed between the soundboard 17 and the frame projection 23. The stiff member 22 is coupled rigidly to bridge point 27 through soundboard 17 and bridge 16. The stiff member 22 is shown as a spring.

The foregoing disclosure has been described for a soundboard, such as might be used in a piano in which the means for radiating sound and the means for providing acoustical stiffness are accomplished by separate means; and in which the soundboard is acoustically relatively tightly coupled to the frame, and vibrates in a diaphragmatic manner.

This invention has been'disclosed as being applicablek to a piano, but it will be apparent to one skilled in the art that the invention is also applicable to other stringed musical instruments.

It will herein be understood, of. course, that these embodiments of the invention have been used for illustrative-purposes only and that various modifications and variations in the present invention may be elected without departing from the spirit and lscope of the novel concepts thereof.

' I claim:

1. A stringed musical instrument comprising:

a frame,

a plurality of strings tensionally supported by said frame, bridge means coupled to said strings,

sound radiator means coupled to said bridge means,

said `sound radiator means being acoustically relatively tightly coupled to said frame, and

stiliening means coupled between said bridge means and said frame, Y whereby the acoustical stiffness at said bridge means is produced primarily by said stiiening means. f 2. A stringed musical instrument in accordance with claim 1 wherein said sound radiator., means is rigidly coupled to said frame.

3. A stringed musical instrument in accordance With claim 1 wherein said sound radiator means is pivotally coupled to said frame.

4. A stringed musical instrument in accordance with claim 1 wherein said sound radiator means is stify coupled to said frame.

y5. A stringed instrument in accordance with claim 1 wherein part of said sound radiator means is rigidiy coupled to said fra-me, and part of said sound radiator is pivotally coupled to said frame.

6. A stringed musical instrument n accordance with claim 1 wherein part of said'sound radiator means is rigidly coupled to said frame, and part of said sound radiator is stillly coupled to said frame.

7. A stringed musical instrument in accordance with claim 1 wherein part of said sound radiator means is pivotally coupled to said frame, and part of said sound radiator is stilfly coupled to said frame.

No references cited.

RICHARD B. WILKINSON, Primary Examiner. C. M. OVERBEY, Assistant Examiner. 

1. A STRINGED MUSICAL INSTRUMENT COMPRISING: A FRAME, A PLURALITY OF STRINGS TENSIONALLY SUPPORTED BY SAID FRAME, BRIDGE MEANS COUPLED TO SAID STRINGS, SOUND RADIATOR MEANS COUPLED TO SAID BRIDGE MEANS, SAID SOUND RADIATOR MEANS BEING ACOUSTICALLY RELATIVELY TIGHTLY COUPLED TO SAID FRAME, AND 